In a motor vehicle with what is known as a start/stop system, the engine serving for propelling the motor vehicle is temporarily stopped or switched off automatically when drive energy for propelling the motor vehicle is not required, for example when the motor vehicle is waiting at traffic lights. Particularly in town traffic, start/stop systems of this type make a considerable contribution to reducing the fuel consumption. They are therefore sometimes used as standard in conventional motor vehicles and, for example, in low-energy vehicles, hybrid vehicles and the like.
If the engine of the motor vehicle at the same time also provides the drive energy for a refrigerating circuit of an air conditioning system, as is generally the case, for example when the engine drives a condenser or compressor of a compression refrigerating circuit by a belt drive, the result of automatically switching off the motor vehicle engine is that the condenser or compressor of the refrigerating circuit of the air conditioning system and therefore the refrigerating circuit of the air conditioning system are likewise temporarily put out of operation. When the compressor is switched off, the temperature of an evaporator operated as a cold exchanger of the air conditioning system therefore rises, so that, with the engine switched off, the air which is to be cooled by the refrigerating circuit and supplied, for example, to a passenger cell becomes warmer, this being detrimental to comfort.
Various embodiments of air conditioning systems have already been proposed in order to solve this problem. Thus, for example, DE 101 24 757 A1 relates to a vehicle air conditioning system in which a cold accumulator is arranged between an air-downstream side of a cooling heat exchanger and an air-upstream side of an air-mixing flap, in order to be cooled by cold air which passes through the cooling heat exchanger. The cold accumulator can in this case be cooled by the cold air from the cooling heat exchanger, and, moreover, the cold accumulator is arranged on the air-upstream side of the air-mixing flap and can be cooled, without being adversely affected by a rotary position of the air-mixing flap.
Furthermore, DE 103 17 039 A1 discloses a device for regulating the air supply with an evaporator and with a heating body, an airstream being apportioned to at least two air ducts. A first air duct conducts the corresponding first part airstream through the evaporator and the heating body, and a second air duct leads the corresponding second part airstream past the evaporator and the heating body. Furthermore, the use of a device of this type in an air conditioning system in a motor vehicle is proposed.
Moreover, DE 102 48 773 B4 describes an air conditioning system for a motor vehicle, the engine of which is switched off correspondingly to an automatic stop-and-go mechanism in order to save energy when the motor vehicle is briefly at a standstill. The air conditioning system has a compression refrigerating circuit drivable via the engine and at least one short-time cold accumulator which is chargeable with cold via the compression refrigerating circuit and which is intended, in particular, to be discharged when the engine is switched off because the motor vehicle is briefly at a standstill. In this operating state, the air conditioning system changes over automatically to a circulating-air operating mode, at least one short-time cold accumulator being arranged in at least one circulating-air duct.
The inventors herein have recognized the above issues and provide a method to at least partly address them. A method for controlling an air conditioning system, in particular an HVAC system for a motor vehicle having a start/stop system, is provided. The method comprises when a refrigerant circuit is in operation and a temperature of an evaporator of the refrigerant circuit is lower than a temperature of a heat exchanger of a heating circuit, transferring heat from the heat exchanger to air passing through the heat exchanger, and when the refrigerant circuit is not in operation and the temperature of the evaporator is higher than the temperature of the heat exchanger, transferring heat from the air passing through the heat exchanger to the heat exchanger.
The transfer of heat from and to the heat exchanger takes place only when it is established that cooling power is required by the air conditioning system. This is the case, for example, when a desired cooling temperature of, for example, a passenger cabin to be cooled in a motor vehicle, is lower than an actual cooling temperature. As a result, the additional load upon the air conditioning system which is required in order to cool the heat exchanger can be restricted to those times when the cold accumulator function could be used anyway, to be precise when the air conditioning system is used for cooling. This ensures especially energy-efficient operation of the air conditioning system in spite of a cold accumulator function which is additionally present.
This affords the advantage that, by the heating circuit being used to cool air provided to the passenger cabin, additional equipment for providing (temporary) cooling function may be dispensed with. According to the disclosure, only the subassemblies or components usually installed in an air conditioning system, in particular an HVAC system, are used, so that no additional structural parts which would result in an increase in weight are required in order to provide the cooling function. Furthermore, retrofitting of existing air conditioning systems without a cold accumulator function can likewise be implemented in an especially simple and cost-effective way by the method according to the disclosure, since the components present in the air conditioning system are to be controlled by the method according to the disclosure.
It should be pointed out that the features listed individually in the patent claims may be combined with one another in any desired technically expedient way and indicate further refinements of the invention. The description additionally characterizes and specifies the invention particularly in conjunction with the figures.